Re: [stella] Supercharger internals...

Subject: Re: [stella] Supercharger internals...
From: bwmott@xxxxxxxxxxxx
Date: Fri, 16 May 1997 09:57:43 -0400 (EDT)
> I have just written a little test program that does SC writing with code
> executed in the VCS RAM and it works. So that does not semm to be the
> explanation.

That's good so it looks like it's counting cycles and not memory accesses.

> What is strange is, that in all my programs I have to use a NOP in the 
> SC writing routine like
> LDX #$1d
> CMP $F000,X
> or the program would crash, because it overwrites some part of the code.

Frogger uses the NOP's as well.  Haven't checked the other games yet.

> But Bob's Etch program, for example, runs perfectly on my system, although 
> it doesn't have the NOPs.

Could you post his code (or just the part that does the write), so I 
could take a look at it?  I've also got a question about bank switching.
Can the read that sets the bank configuration be anywhere in the cart's
memory or does it have to be within the 1000 to 10ff range?  It looks
like most of the games are using the 1000 to 10ff range to set the
bank configuration before accessing 1ff8.  Can someone verify this?

My plans at this point are to use Chris's supercharger code for 
verion 0.7 of Stella.  Most of the games work with it and I'm starting
to run out of time.  For 0.8 I'd like to have "better" Supercharger
emulation.  This will require changing my 6507 emulation to update
cycle counts at every memory access and issue all of the "false" reads
generated by the various addressing modes.  For speed reason's
I'll probably have two 6507 emulators in Stella the current one
and a new high compatiblity one.  Stella will default to the
low compatiblity high speed version, but you'll be able to switch
to the high compatiblity lower speed version by setting a property 
in the stella.vcs file (this can be done on a per-game bases or for
all games).


Bradford Mott (bwmott@xxxxxxxxxxxx)        Computer Science Department           North Carolina State University

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